Different stages in the evolution of backreef sedimentologic regimes are represented in 2 bays behind a barrier reef 0.25-1 mi off the east coast of Carriacou.

In the largest bay, wave transport of reef-produced sediment has formed a shoreward prograding sand body at a depth in equilibrium with sediment grain sizes and prevailing wave conditions. Variations in grain-size distribution on top of and shoreward from the backreef sand flat reflect sorting and mixing, under oscillatory flow, of the mechanically distinguishable lag, rolling, saltating, and suspended sediment populations.

Decrease in the height of the water column, caused by partial filling of the backreef area in the smaller bay, has increased the rate of tidal flow. The sediment grain sizes, bottom depths, currents, and wave conditions are elements of a dynamic equilibrium which, given a steady relative sea level, results in the transport of all reef-produced sediment, up to pebble size, from the backreef area into adjacent deep water, and the maintenance of an equilibrium bottom profile.

The delineated processes and the resulting sediment properties and distribution patterns constitute a model of backreef clastic sedimentation which may be of wide applicability.

End_of_Article - Last_Page 841------------